1. Field of the Invention
This invention relates in general to wrench assemblies and in particular to a wrench assembly for use with a top drive well drilling apparatus.
2. Description of the Prior Art
In the drilling of oil and gas wells, hydraulically powered wrenches are used to make and break connections between tubular members. The wrench assemblies generally used in these applications have a pair of wrenches, one mounted directly above the other. Each wrench grips a joint on either side of the connection, and torque is applied to rotate the wrenches with respect to one another, to make up or break the connection. One such wrench assembly is shown in U.S. Pat. No. 4,348,920 (BOYADJIEFF), issued Sept. 14, 1982. One disadvantage inherent in the prior art has been that the wrenches must be adjusted to accommodate tubular members of different diameters.
A top drive drilling system rotates a drill string from the top, rather than using a rotary table, a kelly, and a kelly bushing. An electric drilling motor is suspended from the drilling rig's conventional swivel and is attached to the top of the drill string. The drilling motor may also be attached to a carriage, which is guided by a pair of vertical tracks. The drilling motor is connected to the drill string by a cylindrical stem, which extends downward from the motor. A top drive sub is the bottom unit of the cylindrical stem, and is the unit to which the drill string is threaded. A wrench assembly is also suspended from the drilling motor, in order to make or break connections between the top drive sub and the drill string. In some prior art top drive drilling systems, the wrench assembly rotates with the drill string and is not removable therefrom. However, there are some top drive well drilling apparatus in which the wrench assembly may be retracted away from the drill string.